The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to prevention of the oil-canning effect at the interior trim surface of an inflatable bladder for an active bolster.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deploying air bag cushions through various openings, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive.
In a typical structure, an active bolster includes a front wall or panel that faces a vehicle occupant and that is attached to a base wall or panel along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. The walls are initially spaced apart while in their non-inflated condition. This allows ingress of the inflation gas in a manner that achieves even inflation across the panel.
As a result of having spaced apart walls, the oil-canning effect can become a problem. Oil canning is the springing in and out of a flat panel perpendicular to the plane of the panel. In addition to a drum-like noise, oil canning is undesirable because it gives a perception of lack of structural quality and integrity. Furthermore, vibrations during operation of a vehicle may become concentrated at the bolster, thereby creating additional noise.
As disclosed in U.S. Pat. No. 8,205,909, the inner field of the bladder walls may contain a plurality of interconnections to improve rigidity and avoid oil canning. Since the front wall moves away from the back or base wall during inflation, the interconnections between the walls must tear or separate during inflation. Thus, the interconnection between the walls must be strong enough to avoid oil canning while being weak enough to avoid interfering with inflation.
The front and base walls of a typical active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They can be blow molded or injection molded. U.S. Pat. No. 8,205,909 discloses pyramidal or conic shaped interconnections projecting from the base wall to contact the front wall. The resulting single point connections make it difficult to control the joint strength and depth during welding of the walls together. It would be desirable to have better control over the strength of the welded joint. In addition, the welding in close proximity to the front wall may cause visible marks on the passenger-facing side of the front wall. It would be desirable to insure a smooth uninterrupted surface of the passenger-facing Class A side.